Telephone-exchange system



S. B., WILLIAMS, In.

TELEPHONE EXCHANGE s'vs'rzm; 7 APPLICATION FILED nmzz. ms. 1,355,635,.Patented Oct. 12,1920.

2 SHEETS-SHEET I.

S. B. WILLIAMS, Jn. TELEPHONE EXCHANGE SYSTEM. wucmou FILED DEC. 21.1918.

v 1,355,635. Patented Oct. 12,1920.

2 SHEETS-SHEET 2.

lawman? 4 QlFrwIiJH 1 JEMIEJE 2 UNITED STATES PIATENT OFFICE.

SAMUEL B, WILLIAMS, JR, 033 IBRGOKLYN, NEIV YQRK, ASSIGNOR TO WESTERNELEC- TR-IC COMPANY, INGORPDRATED, CF NEW YQRK, N. Y., A CORPORATION OFNEW YORK.

TELEPHONE-EXCHANGE SYSTEM.

Specification of Letters Patent.

Patented Oct. 12, 1920.

Application filed December 27, 1918. Serial No. 268,501.

T all whom it may concern Be it known that I, Snsitmn B. WILLIAMS, J r.,a citizen of the United States, residing at Brooklyn, in the county ofKings, State of New York, have invented certain new and usefulImprovements in Telephone-Exchange Systems, of which the following is afull, clear, concise, and exact description.

This invention relates to an improvement in telephone exchange systemsand has particular reference to a semi-mechanical private branchexchange system employing rotary line and selector switches.

An object of the invention is to provide an improved selector switcharranged to serve a plurality of groups of trunks, any one of which maybe selected by a directive movement of the brushes of the switch, theterminals of the trunks in certain of said groups being interspersedeither periodi cally or promiscuously and in such a manner as tomaterially reduce the automatic trunk-hunting operation in the groupsnecessary before finding an idle trunk in the selected group.

Another object is the provision of a terminal bank for a selector switchwherein certain of the terminals are each allotted for determining theselection of one of a plurality of groups of trunks having connectionwith other terminals of said bank. In accordance with this arrangement,the brushes of the switch may, during the directive and automaticmovements thereof in seizing an idle trunk in the selected group, passover the terminals allotted for group selection and also terminals oftrunks in non-selected groups, the test for an idle trunk in theselected group depending upon the finding of two terminals within thesame set simultaneously free from ground.

The inventive idea involved is capable of receiving a variety ofexpressions, one of which, for the purpose of illustrating theinvention, is shown in the accompanying drawings, but it is to beexpressly understood that said drawings are employed merely for thepupose of illustrating the invention as a whole and not to define thelimits thereof, reference being had to the appended claims for thispurpose.

In the drawings, Figures 1 and 2 combined, with Fig. 2 at the right ofFig. 1, illustrate diagrammatically the various circuits of the privatebranch exchange system; Fig. 3 is a diagrammatic view of the trunkingarrangement employed in connection with the invention.

In carrying out the invention, switches of the rotary type havingcontacts arranged in a complete circle are preferably employed forinterconnecting the telephone lines. In Fig. 3, wherein the trunkingarrangement is disclosed, a subscribers substation A is shown inassociation with a line switch B, the brushes of which are caused tomove over the terminal bank by the removal of the receiver at substationA and automatically select an idle trunk, whereby the line is extendedto a first selector switch C. The multiple bank of this switch consistsof a plurality of terminals, certain of which are available for trunksdivided into groups. Two of these groups 0 and 0 are available forautomatically extending a'connection to selecton switches D wheninterconnecting calling and called subscribers within the private branchexchange. The terminals of said groups in the multiple bank of switch Care shown as arranged alternately but it is to be understood that saidterminals may be promiscuously interspersed or disposed at randomwithout departing from the spirit and scope of the invention. Themultiple of the several banks is such that a different trunk appears asthe first trunk in each multiple bank or group of multiple banks. Bythis arrangement, the selectors will not be required to hunt overall'the busy trunks, and the number of busy trunks passed over will beon the average the same when calling through the first group as whencalling through the second group. The other two groups of trunks c and amay be used in establishing connections to a private branch exchangeoperators position and to a central ofiice exchange, respectively. Theterminals in the trunks of each of these groups, in contra-distinctionto the terminals. of groups of trunks c and 0 are preferably arranged inthe ordinary manner.

7 In the final selector switch D, three groups of trunks (Z, (Z and 0Zare shown, and de-' pending upon the number of tens impulses transmittedby the sender at substation A in making an automatic connection to acalled substation, the brushes of the final selector are stepped aroundto one of three terminals. The units digits of numbers in the first twogroups are selected by the dial impulses, but when a number in the lastgroup is called, a group relay operates on the completion of theimpulses for the tens digit, as will appear later, causing thesteppingmagnet of the final selector to automatically step the brushesaround to the last group, and the dialing of the units digit of thenumber then selects the desired trunk in this group.

The operation may be briefly stated as follows: Should a subscriber atsubstation A desire a connection to the central office exchange, theremoval of his receiver will first operate line switch B to seize. anidle trunk. The impulse sender is then manipulated to transmit oneimpulse which will step the brushes of the first selector switch 0 tothe second terminal of the multiple I bank and thus select the group ofcentral office trunks 0 By this selection the terminals of all the othergroups of trunks are rendered non-selectable and the brushes oftheswitch will be stepped over these terminalsand caused to hunt for anidle trunk in the group 0 whereupon the connection will be extended tothe central office.

If it is desired to automatically establish a connection between twosubscribers within the private branch exchange, the calling subscriberwill, by removing his receiver, seize an idle trunk connected to theline switch, and by operating the sender to transmit two or threeimpulses, depending upon which of the groups 0 or c is to be selected,

, the brushes of the selector C will be stepped to the correspondingterminal in the selector bank allotted to the particular group,whereupon a trunk-hunting operation will proceed over the terminals ofthe group of erator, the digit 0 is dialed to send trunks selected. 7 V

7 As previously stated in connection with the trunk hunting in group 0*,the terminals of all the other groups, with the exception of the one inwhich trunk hunting is now proceeding will likewise be madenon-selectable so that should all the trunks in the selected group'bebusy, the brushes of the selector will travel over the groups of trunksc and'o in order that a busy tone will be transmitted to a subscriber atsubstation A. Upon the seizing of atrunk in'either of the two groups 0or 0 the line is extended to the final selector switch which isoperated, as briefly referred to above, connect the calling and calledsubscribers.

To call the private branch exchange opten impulses after a connection"has been extended from the line switch and the brushes of the selectorare stepped to the terminal of the bank in association with the groupsof trunks 0 at which time a trunk-hunting operation would again takeplace to select an: idle trunk leading to the operators position. Again,as described in connection filed on December 27,

r 202, back 'with the trunk-hunting operations in other groups, theterminals thereof, in this instance, will be rendered non-selectable inorder that trunks therein will not be seized.

The trunking arrangement above described forms the subject-matterclaimed in the present application, and the means herein shown anddescribed for establishing the different connections have been disclosedand claimed in a Samuel B. WVilliams and Bert G. Dunham,

Serial No. 268,468.

It is believed that the invention will now be best understood from adetailed description of the operation in establishing a connection froma calling subscriber to a called subscriber and also to central officeand private branch exchange trunks. Upon the removal of the receiver atsubstation A, in initiating a call, line relay 200 of the line switch 13is energized over a circuit from grounded battery, winding of relay 200,back contact and innermost lower armature of'cutofl' relay 201,substation apparatus, upper armature and back contact of relay 201 toground. The marginal stepping magnet 202 is then energized over thecircuit from grounded battery, winding of said magnet, armature and backcontact thereof, front contact and armature of line relay 200 andlowermost brush 203 to ground at the normal terminal thereof, whereuponthe brushes of the switch will he stepped to the second set ofterminals, the trunks of which lead to one of the first selectorswitches Should the selector switch connected to the separateapplication to,

1918, and bearing first test terminal be busy, brush 203 of the groundedbattery, winding of'said magnet,

armature and back contact thereof, front contact and armature of relay200, brush 203, armature and back contact of the line relay of saidother line switch to ground. Magnet 202 being self-interrupting, willagain step the brushes of the line switch over the terminal bank untilan idle trunk is found, whereupon a circuit is established from groundedbattery, winding of magnet contact and armature thereof, winding ofrelay201 in series with said magnet, brush 204, conductor 30%, windingof low resistance relay 307, brush 308 of the selector switch,backcontact and innermost right armature of test relay 303, and rightarmature of relay 301 to ground. ,Magnet 202 being marginal and inseries with relay 7 contact grounds the test terminal and makes thetrunk test busy to all other line switches.

Line relay 309 of the selector switch will energize immediately uponenergization of relay 307 due to a circuit extending from groundedbattery, right winding of relay 309, armature and front contact of relay307 to ground. A circuit for relay 309 will be maintained from groundedbattery, right winding of relay 309, back contact and innermost lowerarmature of cutoff relay 310, lower side of the subscribers line,substation apparatus, upper side of subscribers line, back contact andupper armature of relay 310, left winding of relay 309, brush 311 andcoil 312 to ground. First slow-torelease relay 305 is then energized bya circuit extending from grounded battery, winding of relay 305, andfront contact and armature of line relay 309 to ground. Operation ofrelay 305 establishes a holding circuit for relay 201 extending fromgrounded battery, winding of magnet 202, armature and contact thereof,winding of relay 201, brush 20%, conductor 30% and left armature ofrelay 305 to ground. A dial tone is furnished by coil 312 to inform thesubscriber that he may now operate his sending device. If the subscriberdesires to establish a connection to another P. B. X. subscriber, hewill now transmit two or three impulses, depending upon which group oftrunks c or 0 is to be selected for the trunk-hunting operation.Interruption of the circuit of line relay 309 by the sending devicecauses the armature thereof to vibrate, and upon each retraction acircuit is closed for the stepping magnet 313, extending from groundedbattery, winding of magnet 313, winding of slow-to-release relay 301,right armature of slow-to-release relay 305, which remains energizedduring the line interruptions, back contact and outermost lower armatureof cutoff relay 310 and back contact of the armature of relay 309 toground. The brushes of the selector are stepped from their normalterminals in accordance with the number of impulses sent, and upondeenergization of relay 301 at the termination of the transmission ofimpulses, one of the two roup relays 311 and 315 is energized. ssumingthat the two impulses were sent to select the group of trunks 0', grouprelay 314 will be energized over a circuit extending from groundedbattery, winding of relay 314, brush 308 which now rests upon the thirdterminal in its row, back contact and innermost right-hand armature oftest relay 303 and right armature of relay 301 to ground. Relay 314 inattracting its right armature, energizes test relay 303 over a circuitextending from grounded battery, right winding of said relay, lowermostbrush 316, the third terminal in the row associated with said brush,front contact and right armature of relay 314 to ground. After testrelay 303 is energized, relay 31 1 isheld up until an idle trunk isfound, over a circuit extending from grounded battery, winding of relay314:, left armature and front contact thereof and left armature ofslow-to-release relay 305 to ground Stepping magnet 313 is now operatedover a circuit extending from grounded battery, winding of said magnet,armature and back contact thereof, front contact and outer left armatureof relay 303, front contact and right armature of relay 314 to ground.It is to be noted that the continued energization of relay 31 1 hasremoved the ground at its right armature from the terminals 0f theselected group 0 traversed by the brush 316, but that as long as thetest brush 317 of the selector is moving over busy trunks, test relay303 is held up over a circuit from grounded battery, left winding ofrelay 303, front contact and inner left armature thereof, test brush 317to ground at the busy final selector. It is therefore apparent thatrelay 303 will not release until brushes 316 and 317 engage twoterminals simultaneously free from ground, and consequently steppingmagnet 313 continues to operate until an idle trunk is found. During theenergization of test relay 303, a ground is placed upon the conductor302 except when relay 301 is energized, and this ground provides anadditional guarding potential which will prevent seizure of the selectorby another line switch when the latter is hunting for an idle trunk.lVhen brushes 316 and 317 simultaneously engage two terminals free fromground, test relay 303 will retract its armatures and break the circuitfor stepping magnet 313, and brushes of the selector will come to restupon the selected terminals. Cutoff relay 310 is immediately energizedby the circuit extending from grounded battery, winding of relay 310,back contact and outer right armature of test relay 303, brush 308, backcontact and inner right armature of test relay 303, and back contact andarmature of relay 301 to ground, and the line is thus extended to thefinal selector switch 1). Upon the operation of cutoff relay 310, linerelay 309 and slow-- to-release relay 305 deenergize but the upper andinner lower armatures of relay 310 being of the makeebefore-break type,the connection is cut. through and ground is found at the final selectorfor relay 201 and group relay'314l before the ground at relay 305 isremoved, and said relays thus remain energized.

If all of the trunks in the group are found to be busy, test relay 303remains energized until the brushes of the switch have been stepped ontothe last set of terminals, at which time brush 317, no longer findingground, will cause relay 303 to denergize,

and upon therelease of relay 303, cutoff relay 310 is energized over acircuit extending from grounded battery, winding of relay 310, backcontact and outer right armatureof relay 303, brush 317, inner left-handarmature and back contact of relay 303, normal contact and left-handarmature of relay 301, left-hand armature and alternate contact of relay305 to ground. Upon energization of cutoff relay 310, a busy tone isplaced on the calling line bya circuit extending from grounded battery,right winding of line relay 309, brush 318, lower side of the telephoneline, substation apparatus A, upper side of the telephone line, brush319 and coil of busy tone device'B Z to ground. Through this circuit,relay 309 is held energized until the receiver at substation A isreplaced upon its hook. Line relay 309 then releases whereuponslow-to-release relay 305 will become deenergized. This latter relayopens a circuit for relay 310 at its left-hand front contact abovedescribed. The release of relay 310 closes a circuit from ground,armature and back contact of relay 309, lower armature and back contactof relay 310,,right-hand armature and back contact of relay305, brush316,

right-hand winding of relay 303to grounded battery. The energization ofrelay 303 closes a circuit for stepping magnet 313 fromgroundedjbattery, the winding, armature and back contact of said magnet,left D becomes energized over a circuit extending from grounded battery,right winding of relay 400,.lower side of the telephone line, substation apparatus A, upper side of the telephone line and left windingof relay 400 to ground. In attracting its armature, relay 400 closes theclrcuit for slow-to-release relay 401 which extends from groundedbattery, winding of relay 401, front contact I left armature of relay401.

number is within the groups of trunks (Z or.

and armature of relay 400 to ground. Relay 401 attracts its leftarmature and establishes the ground previously referred to in connectionwith the holding circuit for relay 201 and group relay 314. lVhenrelay401 is energized, relay 402 is also energized over a circuit extendingfrom grounded battery, winding of relay 402, brush 403 in its normalposition, conductor 404 to ground at the If the desired (Z of the finalselector switch D, shown in Fig. 3, the impulse-sending device atsubstation A is operated to transmit either one or nine impulses,depending in which group the trunk-selecting operation is to take place.Assuming that the called numberis in group cl, the sending device isoperated to transmit one impulse, andin response thereto the armature ofrelay 400 will be retracted and close a circuit for the stepping magnet405 extending from grounded batter winding of magnet 405, front contactanc inner left armature ofrelay 402, winding of slow-to-release relay406, back contact and left armature of relay 407, right arma ture ofslow-to-release relay 401 and back contact and armature of relay 400 toground. The brushes of the switch are thereby stepped onto the secondset of terminals. Upon energization of relay 406 in response to theimpulse transmitted a circuit was closed for relay 408 extending fromgrounded battery, winding of said relay and right armature of relay 406to ground, and said relay 408 locked up through its outermost lowerarmature and front contact, armature and backcontact of relay 409 andleft armature of slow-to-release relay 40lto ground. The group of trunkscl has now been se lected, and at the termination of the. impulse,slo'w-to-release relay 406 deenergizes, but relay 402 remains energizedover a cir-' cuit extending from grounded'battery, windingof relay 402,brush 403, conductor 404 and left armature of slow-to-release relay 401to ground. Upon transmitting the units impulses to select the desiredline in the group cl, stepping magnet 405 is again operated over thepreviously described cir-' cuit to step the brushes of the switch. Itisto be noted that as soon as the brush 403 leaves the second terminal,ground will no longer be found for relay 402 at the left armature ofslow-to-release relay 401, but relay 402 will remain energized over acircuit extending from grounded battery, winding of said relay, leftarmature and back contact of group relay 410 and left armature ofslow-to-release relay 406 to ground. Re-

lay 406 remains energized during the transmission of impulses. Steppingmagnet 405 will thus continue to operate in accordance with the impulsestransmitted until the brushes have been stepped upon the desired set ofterminals.- If the line selected is found to bebusy, relay 402 will'findground at the-left armature of slow-torelease relay 406 until the samebecomes deen'ergized at thectermination of the impulses, whereupon thecircuit for relay 402 will be extended from the back contact of the leftarmature of.

relay 406, through relay 407, inner right armature and back contactthereof, front contact and outer left armature of relay 402, brush 411to ground at the busy terminal of the called line. Relay 407 will lockup through its inner right armature to ground at the left armature ofrelay 401. Attraction of the outer right armature of relay 40'?furnishes a busy tone to the calling line extending from groundedbattery, right winding line relay 400, lower side of the subscribersline substation apparatus A, upper side of subscribers line, outer rightarmature of relay 407 and coil 15 Z to ground.

Should the called line be idle, relay 402 releases at the end of theimpulses, since upon deenergization of relay 406, the ground at the leftarmature of the latter relay will be removed. Upon the release of relay402, relay 412 becomes energized over a circuit extending from groundedbattery, winding of relay 412, right armature and back contact of relay402, back contact and innermost right armature of group relay 410, brush413 and back contact and right armature of slow-to release relay 406 toground. Energization of relay 412 extends the line to the selectedterminals and closes a circuit extending from the ringing currentgenerator 414, right winding of relay 409, front contact and inner lowerarmature of relay 40S, lower armature and front contact of relay 412,ringer apparatus at the called substation E, front contact and upperarmature of relay 412 and inner upper armature of relay 408 to ground.Ringing cur rent is thus applied to the line and is also induced intothe secondary winding of relay 409 for the purpose of furnishing aringing tone to the calling station, the circuit for this ringing toneextending from grounded battery, left winding of relay 415, lower sideof the telephone line, substation apparatus A, upper side of thetelephone line, right winding of relay 415 and left winding of relay 409to ground. Relay 409 is marginal and will not attract its armature aslong as the resistance of the substation bell is in its circuit, butwhen the receiver at the called substation E is removed, said relay willbecome energized and break the circuit for relay 408 which extendedthrough the armature and back contact of said relay 409. Relay 408, inreleasing, disconnects the ringing current and closes the talkingcircuit at the innermost upper and lower armatures and back contacts,and conversation may proceed. 7

If the trunk for the called line had been located in group (Z it wouldhave been necessary to transmit nine impulses to the final selector, tostep the brushes thereof onto the tenth terminal shown in the bank ofthe selector D in Fig. 3 and in so stepping the brushes, the operationwould be precisely the same as that set forth above. It should be notedthat no line numbered 91 appears, since the terminal which should havebeen allotted for line No. 91 is, in-

stead, allotted for the selection of group d Should the tens digit ofthe called number be 0, the brushes are stepped around as previouslydescribed until they engage the eleventh terminal shown in Fig. 3,whereupon, as soon as relay 406 releases at the end of the impulses,group relay 410 is energized by a circuit extending from groundedbattery,

winding of relay 410, conductor 416, brush 413, back contact andarmature of relay 406 to ground; The op'erationof relay 410 energizesrelay 402 over a circuit extending from grounded battery, winding ofrelay over a circuit extending from grounded bat- V tery, winding ofrelay 410, front contact and innermost right armature thereof, conductor417, brush 418, back contact and armature of relay 406 to ground. Thestepping operation of the brushes continues until brush 413 reaches theterminal having no connection to the conductor 417, whereupon saidbrushes come to rest on this set of terminals. Relay 410 releases, butrelay 402 continues to be energized over a circuit from groundedbattery, winding of relay 402, brush 403, conductor 404 and leftarmature of slow-to-release relay 401 to ground. In response to theunits impulses, the brushes are again stepped around in the trunkselecting movement in group d in the same manner as previously describedfor calling a number in group cl.

Should the subscriber, after initiating 'a call, hang up his receiverbefore an idle trunk leading to the selector switch has been seized, itwill be apparent that the line switch will continue to hunt for the idletrunk, and upon finding it, cutoff relay' 201 will be energized aspreviously described. Relay 304', being in series with relay 201, alsoenergizes, and at its front contact, closes a circuit for line relay309, which in attracting its armature, energizes slow-torelease relay305, thus grounding conductor 304, leading from cutoff relay 201, at theleft armature of relay 305, instead of at the back contact and rightarmature of relay 301 and thereby shunting relay 307. Release of thisrelay d *nergizesline relay 309, since the circuit has been broken byreplacing the receiver, and armature of relay 309 loses the circuit ofstepping magnet 813 extending over the previously traced circuit,

and the brushes are stepped onto the second set of terminals. Inresponse to the continued deenergization of line relay 309, re-

lay 305 becomes deenergized and after an interval, relay 301 follows.Group relay 320 is then energized over a circuit extending from groundedbattery, winding of relay 320, brush 308, back contact and inner rightarmature of test relay 303, back contact and right armature ofslow-to-release relay 301 to ground. The right armature of group relay320 puts ground on the set ,of test'terminalsassociated therewith, and

closes a. circuit for stepping magnet 313 from grounded battery, windingof magnet 313, armature and back contact thereof,

front contact and outer left armature of relay 303, back contact andleft armature of slow-torelease relay 305 to ground, relay 305 havingbecome deiinergized upon the release of line relay 309. The brushes arenow stepped to the next set of terminals and thisaction, takes placeeach time the brush 316 engages one of the terminals which is connectedto ground at the right armature of group relay 320. lVhen engaging thetest terminals of the different groups 6', 0 and c brush 316 findsground for test relay 303 at the back contacts and armatures of therespective group relays. When relay 320 is energized, ground for thegroup of terminals 0" extends from the armature and backcontact of relay300, outer lower armature and back contact of relay 310, right armatureand back contact of relay 305, outermost and middle left armatures andfront contacts of relay 320 to said terminals. Stepping magnet 313continues to operate until the last set of ter-' minals is reached,whereupon the switch is stepped to normal, as previously described. Itis to be understood that the terminals indicated bydotted lines overwhich brush 316 moves are connected to the other terminals of therespective groups in the same manner as shown in full lines, Upon theshunting of relay 307 as previously .de

scribed, relays 309 and 305 will release,-and

the holding circuit for relay 201 will be broken at the left armature ofrelay 305,

Stepping; magnet 202 will then operate to step the switch B to normalover the circuit extending from grounded battery, winding of magnet 202,armature and back contact thereof, lowermost armature and back contactof relay 201 and brush 205 to ground at the armature and back contact ofline relay 200.

At the termination of a conversatiomin the event that a connection hasbeen established between the calling and called substations, the hangingup of the receiver at substation A releases line relay 400 of the finalselector switch D which also causes slow-to-release relay 401 todeenergize. Relay 410 now energizes over the circuit extending fromgrounded battery, winding of relay 410, brush 418, back contact andright armature of slow-to-release relay 401, back contact andarmature'of relay 400 to ground. Energization'of relay 410 breaks, atits in nermost right armature and back contact, the (ircuit for cutoffrelay 412 causing this relay to release. Stepping magnet 405 nowoperated over the circuit extending from grounded battery, winding ofmagnet 405, armature and back contact thereof, outermost right armatureand front contact of relay 410, brush 418, back contact and rightarmature of slow-to-release relay 401,

back contact and armature of relay 400 to ground, and stepping magnet405 continues to operate until the switch is stepped to its normalposition where the circuits for said magnet and relay 410 are broken.

In order to preventthe selector switch D from being seized during thereturn'of the switch to its normal position, it being understood thatthe busy ground has been removed by the decnergization of slow-toreleaserelay 401, a ground is provided at the middle right armature and frontcontact of relay 410. r

The removal of ground at relay 401 releases group relay 314 of selectorswitch C and places ground on all trunks of the selected groupassociated with said relay and thereby energizes test relay 303 over acircuit extending from grounded battery, right winding of relay 303,brush 316, termnal of the selected trunk, back contact and rightarmature of relay 314 to ground. Test r lay 303, pulling up, opens at isright armature and back contact, the circuit for cutoff relay 310 andcloses the circuit for stepping magnet 313 extending from groundedbattery, winding of magnet 313, armature and back contact thereof, frontcontact and outer left armature of relay 303, back contact and leftarmature of relay 305 to ground, and stepping magnet 3 13 continues tooperate as long as brush 316 engages a terminal which finds ground atthe right armature of relay 314, and will also operate upon eachengagement' of brush 316 with the test terminals associated with grouprelays 315, 320 and 321, which are deenergized. If the brushes haveselected an idle trunk in groups 0 and 0 before reaching the terminal towhich they would be steppediwhen selecting group of trunks c relay 303,said terminal, will be energized by the circuit extending from groundedbattery, right winding of relay 303, brush 316, conductor 322, backcontact and left armature of relay in passing over 305 to ground, andstepping magnet 313 will thus again step the brushes onto the next setof terminals.

Line switch B is also returned to normal by the removal of ground atleft armature of slow-to-release relay 101 which causes the release ofcutoff relay 201, this relay having been held energized by the circuitextending from grounded battery, winding of stepping magnet 202,armature and back contact thereof, winding of relay 201, brush 204,conductor 30st, left armature and back contact of relay 301, backcontact and inner left armature of relay 303, brush 317 and leftarmature of relay 401 to ground. The release of relay 201 energizesstepping magnet 202 over a circuit extending from grounded battery,winding of magnet 20 2, armature and back contact thereof, lowermostarmature and back contact of relay 201 and brush 205 to ground at thearmature and back contact of line relay 200. Stepping magnet 202continues to operate until the brushes thereof engage the normalterminals, whereupon the operating circuit of said magnet will be brokenand the switch will come to rest.

If it is desired to establish a connection to a central office,subscriber at substation A, by removing his receiver, will operate lineswitch B to select an idle trunk leading to one of the first selectors,and upon transitting a single impulse, the brushes of said selector willbe stepped, as previously described, onto the second set of terminalsand thus select the group of trunks c for the trunk hunting operationwhich automatically takes place in the same manner as described inconnection with the extension of a call through group of trunks 0, grouprelay 320, in this instance, becoming energized.

k Should the service of substation A be restricted a conductor 207 isemployed to connect the middle lower armature of cutoff relay 201 of theline switch with brush 206, so that if an attempt is made to call thecentral office from this station, energization of cutoff relay 201 willapply said ground to the magnet 313 will therefore central oilice trunksand cause the same to test busy, said ground extending through the brush206, conductor 323, front contact and middle left-armature of grouprelay 320, which has become energized, to the terminals of the centraloffice trunks.

continue to operate until the last set of terminals is reached,whereupon test relay 303 will be energized over a circuit extending fromgrounded battery, right winding of relay 303, brush 316, the last testterminal, outermost left armature and front contact of re lay 320,conductor 323, brush 206 and middle lower armature and front contact ofrelay 201 to ground, thus causing the stepping Stepping magnet to againoperate and return the switch to normal position. Line switch 13,however, remains in its actuated position as long as the receiver is offthe switchhook and the subscriber may again manipulate his dial to callthe private branch exchange operator.

To establish a connection to the private branch exchange operatorsposition, the sending device at substation A is actuated, after theseizure of an idle trunk by the line switch B, to transmit ten impulsesto step the brushes onto the eleventh set of terminals, whereupon groupof trunks 0 will be selected for the trunk hunting operation, and inthis case group relay 321 will be energized to remove ground from theterminals of the private branch exchange trunks over which test brush316 passes and one of the trunks will be seized in the same manner aspreviously described.

IVhat is claimed is:

1. In a telephone system, a trunking arrangcment for switches includinga bank and groups of trunks terminating in said bank and having theirterminals interspersed, other terminals of the bank being allotted forgroup selection.

2. In a telephone system, a trunking arrangement for switches includinga bank, and groups of trunks terminating in said bank and having theirterminals interspersed, whereby terminals of one group of trunks arepassed over in selecting a trunk in another group, other terminals ofsaid bank being allotted for group selection.

In a telephone system, a trunking arrangement for switches including abank, and groups of trunks terminating in said bank and having theirterminals inter spersed, whereby terminals of one group of trunks arepassed over in selecting a trunk in another group, other terminals ofsaid bank being allotted for group selection, the latter terminals beinginitially passed over in selecting a group of trunks.

it. In a telephone system, a trunking arran ement including a terminalbank, groups of trunks connected to terminals of said bank and havingtheir terminals interspersed, and other groups of trunks connected toother terminals of said bank, certain other terminals of the bank beingallotted for group selection.

5. In a telephone system, a trunking arrangement including groups oftrunks connected to terminals of said bank and having their terminalsinterspersed, and other groups of trunks connected to other ter iinalsof said bank, certain other terminals of the bank being allotted. forgroup selection, one of the latter terminals being arranged betweenterminals of the first named groups.

6. In a telephone system, a trunking ara terminal bank,

rangement including a terminal bank, groups of trunks connected toterminals of said bank and having their terminals interspersed, andother groups of trunks connected to other terminals of said bank,certain other terminals of the bank being allotted for group selectionand being initially passed over in selecting one of said groups.

7. In a telephone system, a trunking arrangement including a terminalbank, groups of trunks connected to terminals of said bank and havingtheir terminals interspersed, and other groups of trunks connected toother terminals of said bank, certain other terminals of the bank beingallotted for group selection and being initially passed over inselecting one of the first named groups.

8. In a telephone system, a trunking arrangement including a terminalbank, groups of trunks connected to terminals of said bank and havingtheir terminals interspersed, and other groups of trunks connected toother terminals of said bank, certain rangement including a terminalbank,

groups'of trunks connected to terminals of said bank and having theirterminals interspersed, and other groups or" trunks connected to otherterminals of said bank, certain other terminals of the bank beingallotted for group selection, one of the latter terminals being arrangedbetween terminals of the first named groups, others of said certainterminals and the terminals of the first named groups being passed overwhen selecting the group of trunks allotted to the terminal which isarranged between terminals of said first named groups.

In witness whereof I hereunto subscribe my name this 23rd day ofDecember, A. D. 1918.

SAMUEL B. WILLIAMS, JR.

